Yes. I mentioned C++ templates, because I don't want to only talk about Haskell. (People make ghc do interesting things, too. And some of them are even not-so-ugly.)

That's when you make a nice set of M4 macros that generate C preprocessor macros that expand to templates.

To be honest the time I did that it actually helped, which I guess goes to show how elegant C++ templates aren't....

Best metaphore ever!